1. Field of the Invention
The present invention relates to an instantaneous voltage-drop compensation circuit, a power conversion apparatus, an instantaneous voltage-drop compensation method and a computer readable medium storing an instantaneous voltage-drop compensation program.
2. Description of the Related Art
There has been commonly used an (AC-DC) power conversion apparatus which converts three-phase alternating current (AC) power to direct current (DC) power. In this power conversion apparatus, there has been also used an instantaneous voltage-drop compensation apparatus which can maintain power supply to a load, particularly when three-phase AC input voltage fails or drops instantaneously (see, for example, Patent Document 1: JP 2004-222447A).
FIG. 9 shows a configuration of a conventional power conversion system 1ζ. As shown in FIG. 9, the power conversion system 1ζ includes a three-phase AC power source 1, a power conversion apparatus 100B and a DC load 9. The power conversion apparatus 100B includes a rectifier 4A which converts the three-phase AC power outputted from the three-phase AC power source 1 to DC power to supply it to the DC load 9, and a condenser unit 8B which is a power storage device as an instantaneous voltage-drop compensation apparatus connected between the rectifier 4A and the DC load 9. A secondary battery has been also used as the power storage device.
In the power conversion apparatus 100B, the rectifier 4A converts the three-phase AC to the DC power in normal operation. In this operation, the condenser unit 8B is charged. When instantaneous voltage failure or drop occurs, the charged power is discharged from the condenser unit 8B to thereby maintain constant output voltage and keep supplying power to the DC load 9.
Three-phase AC is generally connected not only to three-phase equal loads but also to various single-phase loads, however, voltage drops have sometimes occurred in three-phase balanced or unbalanced states under various influences from turn-on of a load, weather, accidental phenomena, or the like.
In the configuration using the power storage device, such as a condenser or a secondary battery, as in the conventional power conversion apparatus 100B, the power storage device requires a large equipment and makes its cost higher. Further, the power storage device has required measures for deterioration with time, had comparatively short apparatus life, and made maintenance load larger.
Accordingly, there was a demand for stable power supply even when instantaneous voltage drop occurs by means of conversion of three-phase AC input power without using such a power storage device. There was also a demand for achieving power factor correction without using the power storage device.